382 



DAVIDSON BLACK 



neirve of the embryo. Fiirbringer (21) found the first spinal 

 nerve (first occipito-spinal) absent in all adult opisthoglossal 

 anurans examined, and Gaupp (1. c.) confirms this observation 

 for the Ranidae which he studied. For this reason I do not 

 understand why Van der Horst has labelled the most rostral 

 rootlet of this series, the first spinal nerve in his reconstruction 

 of this region in Rana catesbeana (1. c, fig. LXXXI). 



R.VIII.desc, 



Nu.XII 



-Nu.X 



R.VIII.desc 



Nu.Xi 



~ --Nu.c.v. 



R.desc.V. 



'r.R.sp.2.r 



Fig. 1 Rana catesbeana. Transverse section through the medulla caudad 

 of the calamus. Abbreviations: F.l.m., fasciculus longitudinalis medialis; 

 F.S., fasciculus solitarius; Nu.c.v., nucleus cornu ventralis; Nu.X., two cells of 

 the caudal end of the motor vagus column; Nu.XII., dorso-medial cell group 

 (nucleus hypoglossus) ; R.desc.V., descending trigeminal fibers in dorsal funiculus; 

 B.sp.2 TO., motor rootlets of second spinal nerve; R.VIII. desc, descending acustic 

 fibers in dorsal funiculus. 



Fig. 2 Rana catesbeana. Transverse section through the medulla at the 

 level of the rostral end of the hypoglossal nucleus. Abbreviations: Nu.X.m., 

 motor vagus nucleus; R.XII., hypoglossal rootlet. Other abbreviations as in 

 figure 1. 



It is evident from the above description of the extent of the 

 dorso-medial nucleus, that it must represent the chief it not the 

 sole place ot origin for the most rostral motor rootlets of the 

 second spinal nerve. The more caudal motor rootlets of this 

 nerve take their origin Irom both dorso-medial and ventro- 

 lateral cell groups ot the cervical somatic motor column. 



The dorso-medial cell group is believed to represent the hypo- 

 glossal nucleus of higher forms for reasons which will be consid- 

 ered subsequently. Thus in figure 2^ the nucleus in question is 



